The present invention relates to a channel structure for an ink jet printhead comprising a channel plate having a plurality of substantially equidistant ink channels formed in one surface thereof, with dams being formed between the adjacent channels, wherein each channel is covered by a portion of a diaphragm supported on said dams and deflectable into the channel by means of an actuator operatively associated therewith.
An example of an ink jet printhead having such a channel structure is disclosed in EP-A-0 820 869. The ink channels are arranged side-by-side and are each connected to a nozzle, so that the nozzles form a linear array with constant spacings between adjacent nozzles. When an actuator associated with one of the ink channels is activated, the portion of the diaphragm engaged by this actuator is deflected into the ink channel, so that the liquid ink contained in this ink channel is pressurized, causing ink droplets to be expelled from the nozzle. The diaphragm portions covering the individual ink channels are formed by a continuous flexible plate which is superimposed on the channel plate and is formed with bumps on the side facing away from the channel plate. The actuators engage only the bumps of the diaphragm, so that the deflection behavior of the diaphragm is improved. In order to optimize the deflection properties of the diaphragm, each bump should be disposed exactly in the widthwise center or middle of the deflectable portion.
Applicant""s co-pending European Patent Application No. 98 200 190 relates to an ink jet printhead in which the diaphragm has a two-layer structure, and the bumps are interposed between the two layers.
In the prior art channel structures the diaphragm has a smooth surface on the side facing the channel plate and is in face-to-face engagement with the top surfaces of the dams separating the individual ink channels. Thus; the position and width of the deflectable portion of the diaphragm is determined by the shape and position of the ink channel in the channel plate. In order to obtain a uniform performance of the various ink channels in terms of drop generation, it is essential that the ink channels are formed in the channel plate with high accuracy, so that only very small manufacturing tolerances can be allowed. As a result, a manufacturing process satisfying these low tolerances is required, and this gives rise to increased manufacturing costs.
It is an object of the present invention to allow for greater manufacturing tolerances in the production of the channel plate without causing deterioration in the uniformity of the drop generation processes in the various ink channels.
This object is achieved by a channel structure wherein the diaphragm is supported on the dams through spacers which define the exact width and position of the deflectable portion of the diaphragm.
Thus, according to the present invention, only the spacers need to be formed with high positional accuracy in order to ensure a correct positional relationship between these spacers and the actuators or bumps. As a result, the channel plate itself may be manufactured with greater tolerances and, accordingly, at lower costs.
Less strict tolerance requirements will generally lead to considerable cost savings, regardless of the process employed for forming the ink channels. In addition, it becomes possible to employ more economic manufacturing processes, such as molding processes, which heretofore have not been acceptable because they could not satisfy the tolerance requirements.
It should be observed that, of course, the nozzles to which each ink channel is connected must be formed with high accuracy. This requirement can, for example, be fulfilled by forming the nozzles in a separate nozzle plate which is then attached to a front face of the channel plate. But even when the nozzles are formed in the channel plate itself, this does not mean, that the level of accuracy required for the nozzles must also be required for the ink channels in their entirety. For example, the ink channels may be formed as grooves cut into the surface of the channel plate with comparatively large tolerances and spaced away from the front face of the nozzle plate in which the nozzles are to be formed. Then, the nozzles may be formed with higher accuracy in a separate manufacturing step, e.g. by laser cutting or the like.
In a preferred embodiment the spacers are formed in one piece with the diaphragm. For example, the diaphragms covering all the ink channels may be formed by a continuous metal foil in which a pattern of grooves and ridges is formed, e.g. by etching, whereby the ridges form the spacers and the thinner bottom portions of the grooves form the flexible portions of the diaphragm. Optionally, bumps to be engaged by the actuators may be formed on the opposite side of the metal foil. Since the metal foil is relatively thin and, correspondingly, the amount of material to be removed by etching or the like is rather small, the increase in manufacturing costs caused by the processing of the metal foil is much smaller than the cost savings achieved in manufacturing the channel plate.
As an alternative, the spacers may also be formed by a separate grid-like member interposed between the diaphragm and the channel plate. The spacers may also be formed in one piece with the channel plate. In this case, the ink channels may at first be formed with a width slightly smaller than the nominal width, so that large tolerances can be allowed. Then, the top surfaces of the dams separating the ink channels may be processed in a more accurate second step in which only small amounts of material are removed from the edges of the dams, e.g. by laser cutting, in order to form the spacers.